I would then poll the survivors monthly, and allow survivors who saw the light and recognized the utter wrongness and evil of Leftism to come back to proper civilization.

I'd do the same poll and tell them that they're going back to civilization, but they'd actually just be walking into a gas chamber that looks like a bus. If anyone believes in leftism after the age of 25, I don't want them in my society. If they renounce evil, their reward is a quick, painless death. The rest can get torn apart and eaten alive by their fellow right side of historinos.